Covered wire and automobile-use wire harness

ABSTRACT

A lightweight insulated electric wire and an automobile wire harness using the same insulated electric wire where the insulated electric wire has a conductor portion including one or more first wires and one or more second wires, which are stranded together. The first wires are constituted by metal wires made from at least one type of metal selected from copper, copper alloy, aluminum and aluminum alloy. The second wires are constituted by metal wires different from the first wires and have a relative permeability of 4.0 or less.

RELATED APPLICATION

This application is a national phase of PCT/JP2004/012658 filed on Sep.1, 2004, which claims priority from Japanese Application No. 2003-309545was filed on Sep. 2, 2003, the disclosures of which Applications areincorporated by reference herein. The benefit of the filing and prioritydates of the International and Japanese Applications is respectfullyrequested.

TECHNICAL FIELD

The present invention relates to an insulated electric wire and anautomobile wire harness having the same insulated electric wire.Particularly, the present invention relates to a lightweight insulatedelectric wire capable of reducing influences of external magneticfields.

BACKGROUND ART

In general, an automobile is equipped with a wire harness (internalwirings) within the vehicle and the wire harness is used for feedingelectricity to electrical equipments within the vehicle, communicationand sensing, etc. Such wire harness is generally constituted of electricwires, protective members and terminals such as connectors which aremounted to the end portions of the electric wires. Conventionally, metalwires constituted mainly of copper are employed as the conductors of theelectric wires.

In recent years, weight reduction of vehicular components has beenadvanced due to demands for fuel consumption reduction and a wireharness is no exception. Also, because of the necessity of resourcessaving and recycles, there is a need for reduction of the amount ofcopper used for electric wires.

There are two important characteristics required for electric wires. Oneof them is the electrical conductivity and the other is the tensilestrength. Copper, which is often used for the conductors of electricwires of the aforementioned wire harness, is a metal material with avery low electrical resistance. Therefore, the electric wires which havethe conductors made of copper can offer sufficient conductivities evenwhen they have relatively small wire diameters. However, in order tomaintain a tensile strength required for electric wires, the wirediameters must be made large to some degree. Consequently, there is thenecessity of reducing the amount of copper used for electric wires whilemaintaining the tensile strength.

On the other hand, there are electric-wire conductors made of stainlesssteel wires with a copper layer on their outer circumferences (refer to,for example, Patent Document 1 and 2). Further, as electric-wireconductors consisting of different types of metal wires strandedtogether, there are stranded wires consisting of stainless steel wiresand copper wires (refer to, for example, Patent Documents 3 and 4).

Patent Document 1: JP-A No. 1-283707

Patent Document 2: JP-B No. 7-31939

Patent Document 3: JP-B No. 63-23015

Patent Document 4: JP-A No. 1-225006

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

As a measure for reducing the amount of copper used in the conductors ofelectric wires in the aforementioned wire harness while maintaining apredetermined tensile strength, there is a possibility to use of metalwires made from metal other than copper which have higher hardness thancopper or metal wires made from copper alloys. As such metals other thancopper, there is, for example, aluminum. However, aluminum has lowerductility than copper and thus has a problem that it will be prone tofracture during crimping of terminals to the end portions of theconductors. Although it is possible to subject aluminum to a thermaltreatment or to alloy aluminum to enhance the ductility of aluminum forpreventing fractures during crimping, these methods do not enable easilyachieving both a high strength and high ductility and thus are notsufficient solutions. Also, when copper alloy is used for electricwires, it is essentially impossible to expect significant enhancement ofthe strength, which imposes limitations on reducing the amount of copperused for electric wires and weight reduction, in view of the strengthrequired for electric wires.

Therefore, it is possible to provide conductors made from a combinationof several types of metals, not from a single type of metal aspreviously described. For example, the conductors described in PatentDocuments 1 and 2 are made of stainless steel wires and a copper layerwhich is formed on their outer circumferences by a plating method or acladding method with the copper layer having a cross section ratio of 5to 70% and therefore have low conductor resistance, high tensilestrengths and excellent ductility. However, for such conductors, it isnecessary to form a copper layer after the fabrication of stainlesssteel wires, which may increase the production time and alsosignificantly increase the cost in the case of forming such a copperlayer by an existing plating method or cladding method.

On the other hand, the conductors described in Patent Documents 3 and 4can be produced with relatively low costs and with enhanced strengths bystranding together metal wires made of copper or the like and stainlesssteel wires. However, in recent years, a great number of electric wiressuch as signal wires and power-supply electric wires (power cables) havebeen mixed and placed in a small space within a vehicle, in order tosupport multi-functions of an automobile. Under the circumstances, thepresent inventors conducted studies and obtained knowledge as follows.That is, an alternating current flowing through a power cable may causevarious deteriorations in the other electric wires placed near the powercable.

More specifically, when electric wires such as signal wires are placednear the aforementioned power cable, while energizing the cable,magnetic fields induced by energizing may cause iron losses (eddycurrent losses) in the other electric wires, which may increase thetemperatures of these electric wires and increase the temperatures ofthe conductors to above the permissible temperature thereof, thusaccelerating the degradation of the insulation layers formed on theouter circumferences of the conductors or causing short-circuitaccidents due to poor insulation before reaching the expected life ofthe insulation layer.

Further, when signal wires are placed near the aforementioned powercable and an alternating current or a high-frequency pulse signal isflowed through the cable, magnetic fluxes are induced in the signalwires, thus resulting in excessive electromagnetic induction noise.

Therefore, it is a main object of the present invention to provide amore lightweight insulated electric wire having an excellent electricalconductivity and a high strength while being capable of reducinginfluences of ambient magnetic fields, in view of the aforementionedcircumstances. It is another object of the present invention to providean automobile wire harness including such an insulated electric wire.

Means for Solving Problem

The present invention attains the aforementioned objects by constitutingthe conductor portion by several types of metal wires and by specifyingthe relative permeability of the wires.

That is, in the present invention, an insulated electric wire includes aconductor portion constituted by one or more first wires and one or moresecond wires which are stranded together. The first wires are metalwires made of at least one metal selected from a group consisting ofcopper, copper alloy, aluminum and aluminum alloy. Further, the secondwires are constituted by metal wires different from the first wires, andare wires having a relative permeability of 4.0 or less.

The present invention employs, as the first wires, a material having lowelectrical resistance and, more specifically, at least one type of metalselected from a group consisting of copper, copper alloy, aluminum andaluminum alloy, in order to ensure an excellent electrical conductivity.Next, the present invention employs, as the second wires, metal wiresdifferent from the first wires, preferably high-strength metal wires, inorder to reduce the amount of copper used therein for reducing theweight and enhancing the strength, such as the tensile strength.

Further, the present invention specifies the relative permeability ofthe constituent materials of the conductor portion in order to suppresseddy current losses, because it is desirable to effectively suppressexcessive temperature rises, particularly at the conductor portion ofthe electric wire due to eddy current losses caused by external magneticfields generated from a power cable since it is placed near the powercable flowing an alternating current therethrough. More specifically,the present invention specifies that the relative permeability of thesecond wires is 4.0 or less.

Hereinafter, the present invention will be described in more detail.

The insulated electric wire according to the present invention includesa conductor portion consisting of first wires and second wires.

(Conductor Portion)

(First Wire)

As the first wires, metal wires made from at least one type of metalselected from a group consisting of copper, copper alloy, aluminum andaluminum alloy are employed. Further, more than a single first wire isemployed. Plural first wires may be employed and, in this case, thefirst wires may be constituted either by the same type of metal wires orby various types of metal wires. This is also applied to the secondwires. When aluminum wires or aluminum-alloy wires are employed as thefirst wires, the weight can be made smaller than when employing copperwires or copper-alloy wires.

As copper wires, it is possible to employ copper wires whose chemicalcompositions consist of copper and unavoidable impurities. Ascopper-alloy wires, it is possible to employ copper alloy wires made ofchemical constituents consisting of copper, one or more elementsselected from a group consisting of Sn, Ag, Ni, Si, Cr, Zr, In, Al, Ti,Fe, P, Mg, Zn and Be, and unavoidable impurities. As aluminum wires, itis possible to employ aluminum wires whose chemical compositions consistof aluminum and unavoidable impurities. As aluminum-alloy wires, it ispossible to employ aluminum-alloy wires whose chemical compositionsconsist of aluminum, one or more elements selected from a groupconsisting of Mg, Si, Cu, Ti, B, Mn, Cr, Ni, Fe, Sc and Zr, andunavoidable impurities.

(Second Wire)

As the second wires, metal wires different from the first wires areemployed. The wires made of metal except copper, copper alloy, aluminumand aluminum alloy described above are employed. Especially,high-strength materials having an excellent tensile strength, etc. aresuitable as the second wires. More specifically, it is possible toemploy stainless steel and titanium alloy, etc. It is also possible toemploy known metal materials or alloy materials. By employing such metalwires having excellent strengths, it is possible to reduce the amount ofcopper contained in the wires for reducing the weight and to enhance thestrength. The present invention employs, as the second wires, wireshaving a relative permeability of 4.0 or less (in a test atmospherewhere there is a magnetic field H of 50 Oe (50×¼π×10³ A/m)). By settingthe relative permeability to 4.0 or less, it is possible to alleviatethe heat generation due to eddy current losses caused by magnetic fieldsfrom the power cable, etc. In order to suppress temperature rises moreeffectively, it is preferable to set the relative permeability to 2.0 orless.

When the other electric wires are placed near an electric wire such as apower cable through which an alternating current is flowed, if theelectric wire such as a power cable is energized, they will generateheat due to eddy current losses caused by influences of magnetic fieldsfrom the cable. In this case, the temperatures of the electric wires(particularly, the conductor portions) are increased and further thetemperatures of other electric wires placed around the electric wiresmay be also increased. Particularly, electric wires used in anautomobile wire harness have extremely small wire diameters and, eventhough each electric wire causes slight heat generation, the entirebundle of electric wires may cause a nonnegligible amount of heat, sincea great number of electric wires, such as about 200 to 400 electricwires, may be bundled together, depending on the type of the automobile.Further, this heat may cause the permissible conductor temperature (forexample, 80° C.) to be exceeded, and the temperature rise may causedegradation of the insulation layer (insulator) and electrical failures,thus resulting in short circuits, etc. As a countermeasure against suchdeterioration, it is possible to employ electric wires made of materialswith higher conductor resistances for suppressing the temperature of theconductor to the permissible temperature or less. However, this methodrequires increasing the cross section of the conductor for providing arequired amount of electric current, which involves increases of theweight and the size of the harness, thereby preventing the weightreduction. As parameters for changing the amount of eddy current losses,there are possibly the frequency of the alternating magnetic field andthe relative permeability of the conductor material, as well as theelectrical conductivity of the aforementioned electric wires. Also, byemploying an insulated material with higher heat resistance or byspacing the power-supply cable apart from the other electric wires, itis possible to alleviate eddy current losses. However, it is generallydifficult to change the frequency of the AC magnetic field since it isrestricted by electric-current specifications, etc. Also, theutilization of an insulated material with higher heat resistance willincrease the cost. Further, spacing the power-supply power cable apartfrom the other electric wires has limitations in terms of space.Therefore, the present invention controls the relative permeability ofthe second wires constituting the conductor portion, in order tosuppress temperature rises due to influences of external magneticfields.

Further, utilization of metal wires with a relative permeability of 1.1or less as the second wires can improve the noise characteristics, inaddition to offering the effect of reducing temperature rises aspreviously described, and therefore is preferable. As previouslydescribed, in recent years, efforts have been made to reduce the weightsand the diameters of electric wires used in an automobile wire harness,in order to support multi-functions of automobiles. As a result, a largenumber of electric wires such as signal wires and power-supply cableshave been mixed and placed in a small space within an automobile. Underthe circumstances, the present inventors conducted investigations andfound the following facts. That is, when a large number of electricwires each including a conductor using magnetic, high-strength steelwires as the second wires are densely placed and, at this state, analternating current or a high-frequency pulse signal flows through apower-supply cable or the like placed near the electric wires, magneticfluxes may be induced thus resulting in the occurrences of excessiveelectromagnetic induction noise in the electric circuit which includesthese electric wires, depending on material properties of steel wire.Further, it was found that, in order to reduce electromagnetic inductionnoise as aforementioned, it is effective to set the relativepermeability to 1.1 or less. Therefore, when it is desired that thenoise characteristics are improved, such as when the electric wiresaccording to the present invention are used as signal wires, etc., it issuggested that the relative permeability be set to 1.1 or less.

As a concrete method for setting the relative permeability of the secondwires to 4.0 or less, for example, it is possible to employ, as achemical composition thereof, a material with a relatively low relativepermeability such as Ti. Also, when γ (austenitic) stainless steel wireswhich are relatively low-price and high-strength materials are employed,it is possible to reduce the relative permeability with manufacturingconditions. More specifically, as a stainless steel, it is possible toemploy, for example, SUS302 or SUS304 which are metastable austeniticstainless steels with relatively low relative permeability. As such astainless steel, a well-known stainless steel may be employed.

Also, it is possible to reduce the relative permeability moreeffectively, by using a stainless steel produced under a specificmanufacturing condition. More specifically, it is possible to select amanufacturing condition which can reduce the amount of strain inducedmartensite, which may cause increases in the relative permeability ofthe austenitic stainless steel. For example, the total reduction in areacan be reduced during the drawing. The amount of strain inducedmartensite is increased with increasing the reduction ratio of drawing,and therefore it is possible to control the amount of induced martensitethrough the reduction ratio (the reduction in area). By reducing thetotal reduction ratio, it is possible to reduce the relativepermeability even for stainless steels with the same compositions. Bysetting the reduction ratio to about 90% or less, the relativepermeability may be made to be 4.0 or less and, by setting the reductionratio to 75% or less, the relative permeability may be made to be 2.0 orless, even though some variations may occur depending on the wirediameter, the die diameter and the die shape. Further, in order to makethe relative permeability to 1.1 or less, the reduction ratio may be setto 40% or less. The smaller the reduction ratio, the more significantlythe strain induced martensite can be suppressed. However, in order toprovide a conductor with a tensile strength of 500 MPa or higher, it ispreferable that the reduction ratio is set greater, to some degree, aswill be described later. For example, when a conductor is formed fromthree copper wires with a wire diameter of about 0.16 mmφ and fourstainless steel wires with the same wire diameter, it is preferable toset the total reduction ratio of the stainless steel wires to 30% ormore. The lower the ambient temperature of the stainless steel duringthe drawing, the more easily the martensite phase is induced. Therefore,it is also effective to increase the working temperature, for example,by interrupting the cooling of the dies during the drawing or byinterrupting the cooling of the capstan used for winding the drawn wire.

When a drawing with a total reduction in area above 40% is performed, byapplying a thermal treatment thereto after the drawing, it is possibleto reduce the strain induced martensite which has been formed by thedrawing. Preferably, the aforementioned thermal treatment is carried outat a temperature below conventional solution treatment temperature (inthe range of over 1000° C. to 1100° C. or less), and more specifically,at a temperature within the range of 800 to 1000° C. By applying such athermal treatment, the relative permeability can be changed inaccordance with the conditions of heat generation and noise reduction.

By applying a drawing with a reduction ratio within a specific range orby applying a specific thermal treatment after the drawing as describedabove, it is possible to reduce the relative permeability withoutcausing significant degradation of the tensile strength. In view ofenhancement of the noise characteristics, the smaller the amount of thestrain induced martensite, the more preferable, and the amount of thestrain induced martensite is preferably 10 vol. % or less and morepreferably 5 vol. % or less.

(Entire Configuration)

The conductor portion is constituted by the aforementioned first wiresand second wires which are stranded together. One or more first wiresand one or more second wires are employed. For example, a single secondwire may be used as a center wire and seven or eight first wires areemployed as outer wires to form a strand wire or plural first wires andplural second wires may be employed to form a strand wire. Also, pluralsecond wires may be stranded together and used as a center wire andfirst wires (outer wires) may be stranded around the outer circumferencethereof. By employing plural second wires, for example, when they areplaced near an automobile engine, it is possible to prevent breaking ofwires due to vibrations of the engine. The greater the amount of thefirst wires included in the conductor portion, the lower the conductorresistance, but the smaller the strength tends to be. On the other hand,the greater the amount of the second wires included in the conductorportion, the higher the strength, but the higher the conductorresistance tends to be. Accordingly, it is preferable to select thenumbers of the first wires and the second wires so that a properelectrical conductivity and a proper strength can be provided. Theinsulated electric wire according to the present invention is suitableas an electric wire in an automobile wire harness, and morespecifically, usable as a signal wire for communication, a power-supplyelectric wire (power cable) for feeding electric power to apparatuses ora earthing wire, etc. Particularly, when it is used as a signal wire inan automobile wire harness, in consideration of voltage drops and thepermissible current value in passing signals or electric currentstherethrough, it is preferable that the conductivity of the conductorportion is within the range of 2 to 60% IACS. Also, when it is used as apower-supply electric wire, it is preferable that the conductivity ofthe conductor portion is 80% IACS or more. It is preferable to combinethe first wires and the second wires so that the aforementionedconductivity can be provided.

Further, when it is used as an electric wire in an automobile wireharness, it is preferable that the tensile strength of the conductorportion is within the range of 400 to 700 MPa. Conventional conductorsconstituted only by copper wires have tensile strengths within the rangeof 250 to 350 MPa. Thus, in the case of conventional conductors, inorder to provide an electric-wire breaking load equivalent to that ofthe aforementioned high-strength conductor, the wire diameter must beincreased. On the other hand, the electric wire according to the presentinvention has an enhanced strength as aforementioned. For example, whena tensile strength of 500 MPa or more is required, the electric wireaccording to the present invention can have a wire diameter which isreduced by at least 20% and by about 70% at a maximum from those ofconductors constituted only by copper wires. Consequently, the presentinvention can increase the strength while reducing the wire diameter.

An insulator (insulation layer) made of vinyl chloride, etc., is formedon the outer circumference of the conductor portion constituted by wireswhich are stranded together. Further, the stranded conductor portion canbe drawn and compressed to further reduce the diameter thereof.

(Terminal Portion)

A terminal portion is mounted to the end portion of the aforementionedconductor portion in order to enable electrically connecting theconductor portion to an external component. In the present invention, aspreviously described, the conductor portion is formed from a combinationof several types of metal. When the conductor is formed from severaltypes of metals as described above, there is a problem which has notbeen induced for conductors formed from a single type of metal, morespecifically, the problem of the occurrence of cell corrosion while theconductor is being energized due to the difference in the ionizationtendency of the metals. Generally, a terminal mounted to the end portionof a conductor portion is made from metal. When the terminal portion isformed from a metal different from the constituent metals of theconductor portion, cell corrosion may occur. However, conventionally,sufficient studies have not been conducted for measures to cases ofcombining different types of metals, particularly to cases where theterminal is also included in the combination.

More specifically, evaluations of corrosion-resistance tests have beenconducted only by exposing only the conductor portion to a corrosiveenvironment and have not been conducted under conditions where currentsand voltages equivalent to those used in actual apparatuses are loaded.Thus, conventionally, material screenings for the materials of theterminal as well as the conductor have not been sufficiently performedin view of cell corrosion. Therefore, the present inventors conductedstudies about materials in view of the aforementioned cell corrosion andobtained the following knowledge.

1. If a current flows through the terminal under a condition where theterminal is exposed to rain water, a cell is formed between thedifferent types of materials which constitute the terminal and theconductor, which may acceleratingly facilitate corrosion of theterminal, thus rapidly degrading the fixing strength between theconductor and the terminal.

2. If corrosion occurs between the conductor and the terminal or betweenthe wires constituting the conductor, this may increase the electricresistance, thus preventing provision of required amounts of current.

Generally, when different types of metals make contact with one anotherand lie in an environment where they can exchange electrons while beingenergized, cell corrosion occurs since these metals have differenttendencies for generating electrons. Particularly, in an automobile wireharness, the contact resistances between the conductor portion and theterminal portion causes large local electric-potential differences and,when the automobile wire harness is exposed to a corrosive environmentsuch as an environment where it is brought into contact with rainwateror water vapor, corrosion tends to significantly advance. Therefore, thepresent inventors conducted studies and obtained knowledge as follows.That is, in order to prevent such cell corrosion, it is desirable toselect materials such that the corrosive electric-potential differencebetween the constituent wires of the conductor portion and the corrosiveelectric-potential difference between the wires and the terminal portionfall within a specific range. Further, in view of suppression of cellcorrosion, it is preferable to select the constituent materials of thefirst wires, the second wires and the terminal portion such that thecorrosive electric-potential difference between the first wires and thesecond wires, the corrosive electric-potential difference between thefirst wires and the terminal portion and the corrosiveelectric-potential difference between the second wires and the terminalportion are all 0.5 V or less. Particularly, it is preferable to employ,as the constituent metal material of the terminal portion, a metaldifferent from at least one of the first wires and the second wires. Inother words, it is possible to employ, for the terminal portion, thesame type of metal as that of the first wires or the second wires,provided that the aforementioned relationships in the corrosiveelectric-potential differences are satisfied. More specifically, it ispossible to employ either the same type of metal as that of the firstwires or a metal which is not selected for the first wires, out of agroup consisting of copper, copper alloy, aluminum and aluminum alloy.Further, it is possible to employ either the same type of metal as thatof the second wires or a metal which is not selected for the secondwires, out of a group consisting of stainless steel, titanium alloy andcarbon steel etc. More specifically, for example, when copper wires areemployed as the first wires, the terminal portion may be made fromeither copper or a copper alloy such as a brass. When stainless steelwires are employed as the second wires, the terminal portion may be madefrom stainless steel. Also, it is preferable to mount the terminalportion by crimping such as staking.

With a wire harness of the present invention including at least aelectric wire of the present invention having the aforementionedconfiguration, it is possible to suppress temperature rises in therespective electric wires due to heat generation caused by externalmagnetic fields, thus preventing temperature rises in the other electricwires placed around the respective electric wires. Consequently, theautomobile wire harness according to the present invention enableseffectively preventing heat generation in the electric-wire bundlecaused by external magnetic fields and thermal degradation caused bytemperature rises.

Effect of the Invention

In the insulated electric wire according to the present invention andthe wire harness according to the present invention which includes suchelectric wire, the conductor portion is constituted by a combination ofseveral types of metals for reducing the amount of copper used therein,thus realizing weight reduction, strength enhancement and costreduction. Particularly, the present invention specifies the relativepermeability of the second wires constituting the conductor portion tosuppress temperature rises caused by influences of external magneticfields, more specifically eddy current losses, thus suppressingdegradation of the insulation layer and occurrences of short-circuits.Also, by further reducing the relative permeability, it is possible toreduce electromagnetic induction noise, thus improving the signalcharacteristics. Further, the present invention specifies the corrosiveelectric-potential differences between the wires made from differenttypes of metals and between the wires and the terminal portion to fallwithin a specific range, in order to effectively suppress cell corrosionto improve the corrosion resistance. In addition, the present inventioncan enhance the recyclability by reducing the amount of copper used forwires. Therefore, the present invention is extremely useful andindustrially valuable, in view of future environmental problems.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described.

Example 1

Insulated electric wires each including a conductor were produced,wherein the respective conductors of the insulated electric wires havedifferent relative permeability. A plurality of such electric wires isbundled into an electric-wire bundle and the electric-wire bundle isplaced near an AC-power-supply cable. Then, the temperature change atthe electric wires was measured when an alternating current was flowedthrough the cable.

The conductor portions utilized for tests had a nine-strandconfiguration consisting of a single second wire as a center wire andeight first wires stranded therearound as outer wires. The respectivefirst wires used therein were copper wires with a wire diameter ofφ0.140 mm made of tough pitch copper (C1100). The second wires usedtherein were stainless steel wires with a wire diameter of φ0.225 mm andthe relative permeability thereof was varied by varying the totalreduction in area. More specifically, a sample No. A with a relativepermeability of 2.0 was produced from a stainless steel made from SUS304by applying a drawing with a total reduction in area of about 70%. Asample No. B with a relative permeability of 4.0 was produced from astainless steel made from SUS304 by applying a drawing with a totalreduction in area of about 90%. A sample No. C with a relativepermeability of 6.0 was produced from a stainless steel made of SUS631by applying a drawing process with a total reduction in area of about70%. These stainless steel wires were used at centers and strandedtogether with copper wires to form conductor portions. The conductivityof the respective conductor portions was determined and the results wereas follows: the sample No. A: 17.5% IACS, the sample No. B: 17.8% IACS,and the sample No. C: 18.4% IACS. Further, the tensile strengths of therespective conductor portions were determined and the results were asfollows: the sample No. A: 552 MPa, the sample No. B: 776 MPa, and thesample No. C: 632 MPa. An insulation layer (with a thickness of 0.20 mm)made from vinyl chloride was formed on the outer circumference of eachof the conductor portions to form insulated electric wires. For eachsample, about 200 insulated electric wires were prepared and were boundby a thermal insulation tape to form a electric-wire bundle. In thepresent example, the length l₁ of the electric-wire bundles 10 was setto 0.3 to 0.4 m.

FIG. 1(A) is an explanation view illustrating a method for measuringtemperature changes in an electric-wire bundle. FIG. 1(B) is anexplanation view illustrating a state where the electric-wire bundle isaffected by a magnetic field generated from an AC-power-supply cable.The electric-wire bundle 10 constituted by plural insulated electricwires 11 bound by a thermal insulation tape 12 as previously describedwas placed in parallel with the power cable 30. In the present example,the center distance l₂ between the power cable 30 and the electric-wirebundle 10 was set to 0.1 m. The power cable 30 used in the presentexample included a copper conductor. While energizing the cable, acurrent which is close to a permissible current was flowed through thecable 30 and the temperature of the copper conductor rose to about 80°C. The cable 30 was connected to an AC power supply 20 capable ofvarying the output frequency, through an energizing current transformer21. The energizing current transformer 21 was connected to a u terminal22 and a v terminal 23 of the power supply 20. On the surface of theelectric-wire bundle 10, the tip of a probe 41 connected to athermometer 40 was placed to enable measuring the temperature of thecenter portion of the electric-wire bundle 10. At this state, when theAC power supply 20 was connected to a plug socket and theAC-power-supply cable 30 was energized (there is illustrated, in FIG.1(B), a state where a current flows from the front to back side of thepaper), the cable 30 generated a magnetic field in the direction of thearrow in FIG. 1(B) and the electric-wire bundle 10 was affected by themagnetic field. More specifically, eddy current loses were generated tocause heat generation, thus increasing the temperature. FIG. 2 shows theresults of the tests. FIG. 2 also shows the results of trialcalculations (curve D). Further, in these tests, the condition ofenergizing the cable 30 was as follows: the current: 100 A and thefrequency: 1000 Hz.

In FIG. 2, the difference between the results of the trial calculationsand the data of the experiments (round marks in FIG. 2) was caused sincethe insulator (the insulation layer and the thermal insulation tape)formed on the electric wires reduced the heat release, thus increasingthe measured temperature rise. However, the trial-calculation resultsand the experiment data reveal that, the smaller the relativepermeability, the smaller the temperature rises. Consequently, it can beproven that it is preferable to make the relative permeability smallerto suppress temperature rises caused by eddy current losses. Morespecifically, when the permissible temperature of the conductor is 80°C., the ambient temperature of the electric wires is 40° C. and thedifference between the permissible temperature and the ambienttemperature, namely 80−40=40 (K), is the permissible temperaturedifference, in order to make the permissible range of the temperaturerise to be 5% or less of the permissible temperature difference, namely40K×5%=2K or less, it is preferable to set the relative permeability to4.0 or less, in taking account of the difference between the trialcalculation result and the experiment data. Further, in order to makethe permissible range of the temperature rise to be 1% or less, namely40K×1%=0.4K or less, it is preferable to set the relative permeabilityto 2.0 or less, in taking account of the difference between the trialcalculation result and the experiment data.

By controlling the relative permeability using the result of theaforementioned tests, it is possible to reduce heat generation andtemperature rises of the electric wire due to external magnetic fieldsand to prevent temperature rises in the other electric wiresconstituting the electric-wire bundle. Therefore, by utilizing theinsulated electric wires according to the present invention, it ispossible to effectively prevent heat generation and thermal degradationin the electric-wire bundle due to external magnetic fields, in the casewhere the electric-wire bundle is used in a wire harnesses, etc.

Example 2

Conductor portions and terminal portions were produced from metalmaterials shown in Table 1 and the terminal portions were mounted to theend portions of the conductor portions to form insulated electric wires.Further, salt spray tests were conducted for the resultant insulatedelectric wires under a condition designated in Table 2. Thereafter, therate of reduction of the fixing-strength of each terminal portion wasdetermined to evaluate the corrosion resistance. Table 3 shows theresults of the tests.

Each conductor was produced by stranding together three first wires andfour second wires, namely a total of seven wires. The first wires andthe second wires both had a wire diameter of φ0.16 mm. Then, afterstranding, an insulation layer (with a thickness of 0.20 mm) made fromvinyl chloride was formed on the outer circumference thereof. Theterminal portions were formed to have an ordinary connector shape usedfor automobile wire harnesses.

Further, the corrosive electric-potential difference between the firstwires and the second wires, the corrosive electric-potential differencebetween the first wires and the terminal portion, and the corrosiveelectric-potential difference between the second wires and the terminalportion were determined. Table 1 shows these corrosiveelectric-potential differences.

TABLE 1 Corrosive electric-potential difference (V) Sample First SecondTerminal Between Between Between No. wire (A) wire (B) portion (C) (A)and (B) (B) and (C) (A) and (C) 1-1 Aluminum alloy Steel Aluminum alloy0.15 0.07 0.08 1-2 Copper Stainless steel Brass 0.25 0.27 0.02 1-3Copper Aluminum alloy Brass 0.61 0.58 0.02 1-4 Aluminum alloy Titaniumalloy Aluminum alloy 0.91 0.98 0.08 1-5 Copper Stainless steel Aluminumalloy 0.25 0.73 0.48 1-6 Copper Steel Stainless steel 0.31 0.56 0.25 1-7Copper alloy Stainless steel Aluminum alloy 0.25 0.88 0.63 1-8 CopperTitanium alloy Brass 0.21 0.23 0.02

The corrosive electric-potential differences (V), in Table 1, werecalculated from the corrosive electric potentials of the respectivemetals within seawater at a room temperature (with a flow velocity of3.0 m/s and a temperature of 20° C.). In Table 1, the copper used forthe first wires was a tough pitch copper (C1100), the copper alloy was a70Cu-30Ni alloy, the aluminum alloy used for the first wires was onedefined in JIS 7075, and the aluminum alloy used for the terminalportion was one defined in JIS 6061. The stainless steel used for thesecond wires and the terminal portions was one defined in JIS SUS304S(with a total reduction in area: 70%) which has been subjected to asoftening (solution treatment) (1150° C.×3 seconds). The titanium alloyused for the second wires was one with compositions constituents (wt. %)of Ti-22V-4Al (DAT51™, manufactured by Daido Steel Co., Ltd.). The steelused for the second wires was SWP-B (wire material SWRS82B) defined inJIS. Further, the relative permeability of the second wires was asfollows: the stainless steel: 1.0012, the aluminum alloy: 1.0002, andthe titanium alloy: 1.0001. The relative permeability of the steel wireswas not measured, but steel wires generally have high relativepermeability within the range of about 5000 to 7000.

In Table 3, the rate of reduction of the fixing strength was determinedby making comparison between the tensile strengths before and after thesalt spray test.

TABLE 2 Temperature during the test 35° C. Concentration of saltwater 5mass % (artificial saltwater) pH 6.8 Specific gravity 1.03 Pressure 99.8kPa Spray time 96 hours Retaining of the thermostat and 80° C. ×humidity humidistat bath after salt spray 93% × 96 hours Load voltage 15V

TABLE 3 Sample No. Rate of reduction of fixing strength (%) 1-1 0 1-2 01-3 54 1-4 Incapable of measurement (elution of all the aluminum) 1-5 861-6 50 1-7 Incapable of measurement (elution of all the aluminum) 1-8 0

After the spray tests, the states of the respective insulated electricwires were inspected. As a result, slight corrosion was observed in thesamples Nos. 1-1, 1-2 and 1-8, which exhibited a corrosiveelectric-potential difference of 0.5V or less between the first wiresand the second wires, between the first wires and the terminal portionand between the second wires and the terminal portion. However, asdesignated in Table 3, the fixing strengths of the samples were notdegraded at all, which revealed that they had excellent corrosionresistance.

On the contrary, corrosion was significantly advanced in the samplesNos. 1-3 to 1-7 which exhibited a corrosive electric-potentialdifference above 0.5 V, between the first wires and the second wires,between the first wires and the terminal portion or between the secondwires and the terminal portion. Particularly, since these samples Nos.1-3 to 1-7 exhibited a corrosive electric-potential difference above 0.5V between the second wires and the terminal portion, the fixingstrengths of their terminal portions were significantly degraded due tocorrosion, as shown in Table 3. Further, in the samples Nos. 1-3 and1-4, significant corrosion was observed between the first wires and thesecond wires, as well as between the second wires and the terminalportion. Further, in Table 3, for the samples Nos. 1-4 and 1-7, the rateof reduction of the fixing strength is indicated as “incapable ofmeasurement,” since corrosion was advanced and thus the aluminum alloyconstituting the first wires was eluted, thus leaving only the titaniumalloy wires and the stainless steel wires of the second wires.

Further, before the spray test, the conductivity of the conductorportion and the tensile strength of the conductor portion weredetermined for the samples Nos. 1-1, 1-2 and 1-8 and the followingresults were obtained: the sample No. 1-1: 32% IACS and 603 MPa, thesample No. 1-2: 38% IACS and 586 MPa, the sample No. 1-8: 40% IACS and592 MPa. From these tests, it was proven that, by setting the relativepermeability of the second wires to a specific value and also byconstituting the terminal portion by a specific material, it is possibleto provide an electric wire being capable of suppressing temperaturerises therein and having excellent corrosion resistance.

Example 3

Stainless steel similar to that of the second wires used in the sampleNo. 1-2 in the second example was prepared and the relative permeabilityof the stainless steel was varied. In the present example, the totalreduction in area during the drawing was varied within the range of 0 to70% to vary the relative permeability and the results are shown (FIG.3). Further, the heating temperature during the softening after thedrawing (with a total reduction in area of 70%) was varied within therange of 900 to 1150° C. to vary the relative permeability and theresults are shown (FIG. 4). In the softening, the holding time was 3seconds for each temperature.

As a result, as shown in FIG. 3, it was proven that the relativepermeability μ was able to be varied by varying the reduction in areaduring the drawing. Particularly, by setting the total reduction in areato 40% or less, the relative permeability μ can be made to be 1.1 orless.

Further, as shown in FIG. 4, by changing the heating temperature duringthe softening after the drawing, the relative permeability μ can bechanged. Particularly, by setting it to 1000° C. or higher, the relativepermeability μ can be made to be 1.1 or less, even when the totalreduction in area is above 40%.

Signal wires were produced similarly to the sample No. 1-2 in the firstexample, by employing the stainless steel wires with varying relativepermeability as the second wires, and by using the copper wires used inthe sample No. 1-2 in the second example as the first wires. Further,these signal wires were wound into a coil shape together with anAC-power-supply electric wire (power cable) used in a conventionalautomobile wire harness and they were housed within a box which wasshielded from external magnetic fluxes. At this state, an alternatingcurrent signal was flowed through the AC-power-supply electric wire andthe probability of errors was determined for the signal wires. Table 4represents the total reduction in area during the drawing for thestainless steel wires used for the second wires, the heating temperatureduring the softening, the relative permeability and the errorprobability of the signal wires. The error probability was defined asthe probability that the amplitude of a high-frequency signal wasreduced to 70% or less of a predetermined amplitude.

TABLE 4 Heating Error Sample Reduction temperature × time Relativeprobability No. in area % ° C. × seconds permeability % 2-1 0 Null 1.0040 2-2 10 Null 1.005 0 2-3 40 Null 1.098 5 2-4 70 Null 1.564 40 1-2 701150° C. × 3 seconds 1.003 0 2-5 70 1000° C. × 3 seconds 1.057 0 2-6 70 900° C. × 3 seconds 1.465 44

As shown in Table 4, when a metastable austenitic stainless steel suchas SUS304 is used, if a drawing is performed with a total reduction inarea of 40% or more, signal errors will tend to occur. This isconsidered to be caused by significant increase of strain inducedmartensite due to the drawing. The amount of the strain inducedmartensite was actually determined. As a result, the amount thereof was26 vol. % in the sample No. 2-3 while it was 57 vol. % in the sample No.2-4, which was greater.

Further, as shown in Table 4, even when a metastable austeniticstainless steel as SUS304 is employed and a drawing is performed with atotal reduction in area of 40% or more, it is possible to prevent theoccurrence of signal errors by subsequently applying a thermaltreatment. This is considered to be due to that the strain inducedmartensite which has been induced during the drawing can be reduced bythe thermal treatment. The amount of strain induced martensite wasactually determined. As a result, the amount thereof was 25 vol. % inthe sample No. 2-5, which was reduced from that in the sample No. 2-4.

Consequently, it has been proven that, when stainless steel wires areemployed as the second wires, it is possible to suppress temperaturerises due to eddy current loses and to effectively prevent signalerrors, by controlling the amount of strain induced martensite throughthe manufacturing condition such as the reduction ratio and the thermaltreatment temperature and the like, namely by controlling the relativepermeability to within a specific range.

Further, the conductivity of the conductor portion and the tensilestrength of the conductor portion were determined for the samples Nos.2-1 to 2-6 and, as a result, the following results were obtained: thesample No. 2-1: 38% IACS and 543 MPa, the sample No. 2-2: 38% IACS and562 MPa, the sample No. 2-3: 38% IACS and 591 MPa, the sample No. 2-4:38% IACS and 655 MPa, the sample No. 2-5: 38% IACS and 607 MPa, and thesample No. 2-6: 38% IACS and 681 MPa. Thus, it was proven that thesamples Nos. 2-1 to 2-6 were sufficiently usable as signal wires for anautomobile wire harness, for example. Particularly, it was proven thatthe samples Nos. 2-1 to 2-3 and 2-5 were more suitable for an automobilewire harness since they exhibited low signal-error probabilities.

INDUSTRIAL APPLICABILITY

The insulated electric wire according to the present invention is mostsuitable for use as electric wires for an automobile wire harness. Morespecifically, it is usable as signal wires for communication,power-supply electric wires for feeding electric power to apparatuses orearthing wire, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is an explanation view illustrating tests conducted in a firstexample and illustrating a method for measuring temperature changes inan electric-wire bundle.

FIG. 1(B) is an explanation view illustrating a state where theelectric-wire bundle is affected by a magnetic field generated from anAC-power-supply cable.

FIG. 2 is a graph illustrating the relationship between the relativepermeability and the temperature rise in a signal wire.

FIG. 3 is a graph illustrating the relationship between the totalreduction in area during the drawing and the relative permeability.

FIG. 4 is a graph illustrating the relationship between the thermaltreatment temperature of a solution treatment after the drawing and therelative permeability.

EXPLANATIONS OF LETTERS OR NUMERALS

10: electric-wire bundle

11: insulated electric wire

12: thermal insulation tape

20: AC power supply

21: energizing current transformer

22: u terminal

23: v terminal

30: power cable

40: thermometer

41: probe

1. An insulated electric wire, comprising: a conductor portionconsisting of one or more first wires and one or more second wires whichare stranded together; wherein said first wires are constituted by metalwires made from at least one type of metal selected from a groupconsisting of copper, copper alloy, aluminum and aluminum alloy, saidsecond wires are constituted by stainless steel, and have a relativepermeability of 1.1 or less, and content amount of process inducedmartensite of 26% by volume or less, and the tensile strength of theconductor portion is 400 MPa or more and 700 MPa or less.
 2. Theinsulated electric wire according to claim 1, wherein the content amountof the strain induced martensite of said second wires is 10% by volumeor less.
 3. The insulated electric wire according to claim 1, whereinthe stainless steel is metastable austenite stainless steel.
 4. Theinsulated electric wire according to claim 1, wherein a terminal portionis provided at the end portion of the conductor portion, said terminalportion is made from a metal different from at least one of the firstwires and the second wires, and the corrosive electric-potentialdifference between the first wires and the second wires, the corrosiveelectric-potential difference between the first wires and the terminalportion and the corrosive electric-potential difference between thesecond wires and the terminal portion are all 0.5 V or less.
 5. Theinsulated electric wire according to claim 1, wherein the conductorportion has a conductivity within the range of 2 to 60% IACS.
 6. Anautomobile wire harness comprising the insulated electric wire accordingto any one of claims 1 to 5.